Databases typically have a redundant copy of data for fault tolerance. If a primary copy of data goes down, a mirror copy of data may take its place so that the database's downtime is minimized.
When bringing back the primary copy, conventional methods typically copy over all the data from the mirror. This method may be acceptable in small databases, or in environments where the transfer time is not an issue. However, this method does not scale very well. In large databases, it may be expensive and costly to transfer large amounts of data from the mirror to primary, or vice versa.
Some conventional methods also require the mirror copy to be non-active, or offline, when transferring data to the primary. This, too, may be prohibitively expensive. For example, a database which keeps track of commercial transactions may cost a company millions of dollars in revenue if the database is offline for a prolonged period of time.
There is a need, therefore, for an improved method, article of manufacture, and apparatus for resynchronizing primary and mirror copies.